Poplocks are a very clever system for making movable papercraft fastenings with die-cutting and folding. The Paper Pose-Ables site has a bunch of downloadable papercraft toys you can print out and make, as well as pre-cut/scored kits you can buy, for making fabulous poseable robots and other cool figures.
The Pose-Ables people came out to one of my signings last month and gave me a couple of GUPP-E robots, which I've put together this week, with help from my five-year-old daughter Poesy. The robots were fun to put together -- just intricate enough to be challenging without being frustrating -- and the Poplocks system really makes for a great, semi-rigid joint for the toys.
The Poplocks themselves are CC licensed for use in your own models.
The Poplock pushes the two pieces of paper tightly together, creating lots of friction! It can also stay put, and won't pop out on it's own, unless a good amount of force is used to bend it out of place.
Combine the Poplock Wedge with the special Locking Flaps hole, and you will create a nigh-invincible connection. Seriously, you won't be able to get the connection apart with torsion or pulling forces unless you rip or crumple the parts. Even then, the Poplock will probably stay put... holding two mangled pieces of paper together!